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 #include &lt;QtGui&gt;

 #include &quot;bubble.h&quot;

 Bubble::Bubble(const QPointF &amp;position, qreal radius, const QPointF &amp;velocity)
     : position(position), vel(velocity), radius(radius)
 {
     innerColor = randomColor();
     outerColor = randomColor();
     updateBrush();
 }

 void Bubble::updateBrush()
 {
     QRadialGradient gradient(QPointF(radius, radius), radius,
                              QPointF(radius*0.5, radius*0.5));

     gradient.setColorAt(0, QColor(255, 255, 255, 255));
     gradient.setColorAt(0.25, innerColor);
     gradient.setColorAt(1, outerColor);
     brush = QBrush(gradient);
 }

 void Bubble::drawBubble(QPainter *painter)
 {
     painter-&gt;save();
     painter-&gt;translate(position.x() - radius, position.y() - radius);
     painter-&gt;setBrush(brush);
     painter-&gt;drawEllipse(0, 0, int(2*radius), int(2*radius));
     painter-&gt;restore();
 }

 QColor Bubble::randomColor()
 {
     int red = int(205 + 50.0*qrand()/(RAND_MAX+1.0));
     int green = int(205 + 50.0*qrand()/(RAND_MAX+1.0));
     int blue = int(205 + 50.0*qrand()/(RAND_MAX+1.0));
     int alpha = int(91 + 100.0*qrand()/(RAND_MAX+1.0));

     return QColor(red, green, blue, alpha);
 }

 void Bubble::move(const QRect &amp;bbox)
 {
     position += vel;
     qreal leftOverflow = position.x() - radius - bbox.left();
     qreal rightOverflow = position.x() + radius - bbox.right();
     qreal topOverflow = position.y() - radius - bbox.top();
     qreal bottomOverflow = position.y() + radius - bbox.bottom();

     if (leftOverflow &lt; 0.0) {
         position.setX(position.x() - 2 * leftOverflow);
         vel.setX(-vel.x());
     } else if (rightOverflow &gt; 0.0) {
         position.setX(position.x() - 2 * rightOverflow);
         vel.setX(-vel.x());
     }

     if (topOverflow &lt; 0.0) {
         position.setY(position.y() - 2 * topOverflow);
         vel.setY(-vel.y());
     } else if (bottomOverflow &gt; 0.0) {
         position.setY(position.y() - 2 * bottomOverflow);
         vel.setY(-vel.y());
     }
 }

 QRectF Bubble::rect()
 {
     return QRectF(position.x() - radius, position.y() - radius,
                   2 * radius, 2 * radius);
 }</pre>
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